The invention relates generally to orifice plates for fluid jet printers and more particularly, to a method for depositing a non-wetting coating on the surface of the orifice plate without clogging the fluid jetting orifices.
Fluid jet printers produce images on a substrate by ejecting fluid drops onto the substrate in order to generate characters or images. Certain fluid jet printers are of the xe2x80x9ccontinuousxe2x80x9d type, where drops of fluid, such as ink, are continuously jetted through an orifice of a print head in a charged state. The charged droplets of are then electrostatically directed onto the printing substrate when printing is desired and into a gutter when printing is not desired
Another type of a fluid jet printer is an xe2x80x9con demandxe2x80x9d type printer. Drops of fluid, such as ink, are selectively jetted through an orifice of a print head when printing is desired and not jetted when no printing is desired.
An ink storage chamber is commonly connected to the print head via an ink flow passageway, to provide a constant flow of ink to the printer head. Ink jet heads generally employ capillary action between the ink and passageways in the ink jet head to position ink at the proper location in the head for proper jetting and drop formation. High pressure outside the print head can undesirably overcome the capillary action and force ink back into the head. Low pressure outside the print head can undesirably draw ink out of the head.
Ink is generally ejected through an orifice formed through an orifice plate. Buildup of material at the orifice can affect surface tension interactions, drop formation and disrupt proper operation. Ink buildup at the orifice surface can also attract dust, paper fibers and other debris and lead to clogging of the orifice. Ink present at the surface of the orifice can also lead to smearing and require increased distance between the orifice and the printing substrate, which leads to a decrease in print quality. Thus, it is desirable for the surface of the orifice plate to be non-wetting with respect to the fluid jetted through the orifice.
It is also advantageous for the inside of the ink passageways to be wetting. If the inside is wetting, ink will tend to coat all of the internal surfaces, proceed to a proper position in the print head and help air to exit from the ink passageways within the print head. If there is air inside the print head or the ink does not travel to the proper location, the jets might not operate properly.
Various commonly known non-wetting coating methods have proved inadequate. The holes in the orifice plate are generally small, commonly about 0.002 inches in diameter. This makes them very difficult to mask off during a coating operation. Thus, some methods that involve coating the surface of the orifice plate will inadvertently coat the inside of the orifices, leading to either clogging or improper wetting properties within the fluid passageway. Some non-wetting coating materials tend to be removed from the surface of the orifice plate either through contact with ink or when the orifice plate is cleaned with various cleaning solvents used to clean dried ink from the orifice plate.
Accordingly, it is desirable to provide an improved method of coating an orifice plate, to provide a non-wetting surface on the outside of the plate, while not clogging the orifices or coating the inner passageways within the orifices with the non-wetting material.
Generally speaking, in accordance with the invention, a method for coating an orifice plate and an orifice plate having a non-wetting coating thereon is provided.
To form the plate, material having non-wetting characteristics can be provided as a surface of a transfer block. The non-wetting material preferably comprises Teflon (PTFE). In one embodiment of the invention, the transfer block is a relatively soft material, which preferably has good heat transfer properties, such as aluminum. In another embodiment of the invention, the transfer block is made of the non-wetting material or has a thick layer of the non-wetting material on at least one surface. In another embodiment of the invention, a thin layer of the non-wetting material is disposed on the surface of a transfer block. In still another embodiment of the invention, the non-wetting material is disposed on the surface of a conformable material, such as a heat resistant elastomer, such as silicone.
The surface of the transfer block comprising the non-wetting material can be pressed against the orifice plate, preferably under heating conditions. In one embodiment of the invention, the non-wetting surface is pressed against a secondary transfer block to coat the secondary transfer block with the non-wetting material and the coated surface of this second block is pressed against the orifice plate, preferably under heating conditions. Additional transfers can be made in order to achieve a coated surface having the appropriate thickness and other characteristics to be transferred to the surface of the orifice plate, substantially to the edge of the orifice, but substantially not being deposited on the inner surface of the orifice plate defining the orifice. In this manner, proper printing operation can be achieved, but ink and other debris can be kept off the surface of the orifice plate.
In yet another embodiment of the invention, a layer of the non-wetting material is provided as the surface of a transfer block. A spacer plate having at least one opening formed therein is positioned against the orifice plate wherein the at least one opening of the spacer plate is aligned with the orifice, a group of orifices or a plurality of orifice groups in the orifice plate. The surface of the transfer block comprising the non-wetting material can be pressed against the spacer plate under heating conditions so that the spacer plate is positioned between the transfer block and the orifice plate. The non-wetting material is vaporized and transfers to the orifice plate where it deposits. Multiple transfers can be made from the same transfer block, to multiple orifice plates, in order to achieve coated surfaces of the orifice plates having the appropriate thickness and other characteristics, substantially to the edge of the orifices, but substantially not being deposited on the inner surfaces of the orifice plates defining the orifices. In this manner, proper printing operation can be achieved, but ink and other debris can be kept off the surface of the orifice plate.
The temperature at which transfer is effected depends on the thermal properties and heat resistance of the material to be transferred. If Teflon is to be transferred, temperatures over 400xc2x0 F., more preferably over 500xc2x0 F. and most preferably in the 550xc2x0 F.-650xc2x0 F. range can be used. Care should be taken so as not to heat the orifice plate and/or material to be transferred, to such an extent that the non-wetting material begins to degrade. The heat and pressure (if any) should be sufficient to transfer the non-wetting material onto the surface of the orifice plate without clogging or coating the orifices or adversely affecting the operation of the print head.
Accordingly, it is an object of the invention to provide an improved method for providing a non-wetting coating on an orifice plate for a fluid jet printer.
Another object of the invention is to provide an improved orifice plate for a fluid jetting print head, having a non-wetting coating on the outside surface thereof.